Such arms comprise a plurality of articulated links. In some, all of the articulations are ‘universal’, or at least may bend in more than one plane, so that the arm can adopt various shapes. Others have hinge joints, which give a stiffer structure, but which are more limited in movement. Hinge joints can be used at alternating angles (eg perpendicular to each other) to improve flexibility of shape. These require separate control of each articulation. Where it is necessary for the arm to navigate a curved surface or other non-planar surface, it has been considered necessary to use an arm with universal joints. Such surfaces may for example include the interior surface of a body cavity such as the stomach.
There is a need for inspecting the condition of gas turbine blades, and also for repairing them. In the past it has been necessary to provide apertures in the casing of the engine at intervals so that any blade can be inspected. Alternatively it has been necessary to dismantle the engine. It would be advantageous to eliminate the need for this.
A problem with inspecting a compressor from the outside via the air intake is that the blades form obstacles to any tool inserted therein. Moreover the position of these obstacles varies depending upon the build of the machine as well as the position in which they have come to rest after the engine has been stopped. Also, the cross-sectional shape of each blade varies from the base to the tip such that the unobstructed space between the blades is a complex volume, which changes in cross-sectional shape depending upon the distance away from the rotor surface.